1. Field of the Invention
The present invention relates to an apparatus and method for improving the efficiency of a power amplifier. More particularly, the present invention relates to an apparatus and method for improving the efficiency of power amplification by improving a supply modulated amplifier. The supply modulated amplifier refers to a power amplifier amplifying an input signal using a supply voltage modulated considering the amplitude of the input signal.
2. Description of the Related Art
Along with the growth of a wireless communication technology, a demand for transmission of various multimedia signals is suddenly increasing. In addition, the growth of the wireless communication technology has increased the demand and need for a fast transmission. As fast transmission is required even in the mobile environment, a concern about a 4th-Generation (4G) communication system is suddenly increasing.
The 4G communication system requires a faster transmission speed, a wider bandwidth, and a higher Peak to Average Power Ratio (PAPR) than an existing communication system provides. According to such requirements, a transmit end of the 4G communication system employs a scheme of amplifying an input signal using a supply voltage modulated considering the amplitude of the input signal. For example, to amplify the input signal using the supply voltage modulated considering the amplitude of the input signal, the transmit end employs an Envelope Elimination and Restoration (EER) amplification scheme, an Envelope Tracking (ET) amplification scheme, a polar amplification scheme, and the like.
A supply modulated amplifier can obtain high efficiency by reducing a power loss through a variation of a supply voltage of a power amplifier dependent on an output power of the power amplifier.
In a case of using the ET amplification scheme, the supply modulated amplifier is constructed as illustrated in FIG. 1.
FIG. 1 illustrates a construction of a supply modulated amplifier according to the related art.
Referring to FIG. 1, the supply modulated amplifier of an ET amplification scheme includes a baseband signal processor 100, an envelope generator 110, a supply modulator 120, a Radio Frequency (RF) processor 130, and a power amplifier 140.
The baseband signal processor 100 generates In-phase/Quadrature-phase (I/Q) data and outputs the I/Q data to the RF processor 130. The RF processor 130 converts the I/Q data provided from the baseband signal processor 100, into an RF signal and provides the RF signal as an input signal of the power amplifier 140.
The envelope generator 110 generates an envelope signal corresponding to the I/Q data provided from the baseband signal processor 100. The supply modulator 120 determines a supply voltage of the power amplifier 140 depending on the envelope signal generated in the envelope generator 110.
The power amplifier 140 amplifies an input signal provided from the RF processor 130 using a supply voltage provided from the supply modulator 120, and outputs the amplified input signal.
As described above, when modulating a supply voltage of the power amplifier depending on an envelope signal corresponding to an input signal of the power amplifier, the supply modulated amplifier can reduce a power loss as illustrated in FIG. 2.
FIGS. 2A and 2B illustrate a supply source of a supply modulated amplifier according to the related art. More specifically, FIG. 2A illustrates an output waveform for a power amplifier receiving an applied fixed supply voltage. FIG. 2B illustrates an output waveform for a supply modulated power receiving an applied supply voltage varied depending on the amplitude of an input signal.
Referring to FIGS. 2A and 2B, the supply modulated amplifier receiving an applied supply voltage varied depending on the amplitude of an input signal can reduce a power loss 210 more than the power amplifier receiving an applied fixed supply voltage. For example, as illustrated in FIGS. 2A and 2B, the power loss 200 for the power amplifier receiving the applied fixed supply voltage is greater than the power loss 210 for the power amplifier receiving an applied supply voltage varied depending on the amplitude of the input signal. The power loss from the power amplifiers may be dissipated as heat.
Generally, the supply modulated amplifier provides a supply source, which is modulated considering the amplitude of a transmission signal, only to a high power amplifier for amplifying a signal of a high power level to enhance the efficiency of a high power level region of high output power. In this case, in a low power level region of low output power, the supply modulated amplifier cannot get the profit of a technology of modulation of a supply voltage of a power amplifier and therefore, needs a way of enhancing the efficiency of power amplification in the low power level region.
Therefore, a need exists for a system and method for improving the efficiency of a power amplifier.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.